In the beginning there was Big Bird, and children saw him and said he was good. And in one of those rare moments of inter-generational concord, parents saw him and said he was good too. And so it came to pass that Ernie, Bert, Mr Snuffleupagus and the other characters of Sesame Street were welcomed into liberal homes and hearts, first in America and then around the world.

Progressive parents who denied their boys access to toy guns and forbade their daughters Barbies, only to find their offspring escaping to friends' houses to play war and dress dolls, finally found a tool for ethical and educational child-rearing that worked. Unlike broccoli and piano lessons, here was one of those rare things that parents thought was good for their children and that their children actually enjoyed. Recently, however, even this simple relationship has been violated. In the past year Sesame Street has come under fire in the Middle East, been subject to intense criticism and scrutiny in the US Congress from rightwing republicans, and is struggling to make itself understood within the sectarian atmosphere of Northern Ireland.

A tragic indication that even the most noble attempts to inculcate children with the basic principles of universal humanism - that, whatever our differences, we are more alike than unalike -will founder against the rocks of deeply held prejudices of their parents. Proof, at the very simplest level, that while culture can confront prejudice, only changes in the material conditions that gave rise to it can ever eliminate the discrimination that feeds it.

If the Golden Arches Theory of Conflict Prevention claimed that no two countries that had a McDonald's had ever gone to war with each other, then this is the Sesame Street Theory of Conflict Resolution: that no two communities can claim peace unless a locally specific format of Sesame Street can be screened to their children.

It is, admittedly, a major claim for a children's programme, launched in America in 1969 with particular attention to disadvantaged pre-school children in urban areas. But its remit soon widened. It intertwined the effective teaching of basic literacy and numeracy with values, such as sharing and tolerance, which do not make their way to school league tables.

By dealing directly, yet sensitively, with issues like death and divorce, it encouraged emotional intelligence as an essential part of a child's education. By deliberately but unselfconsciously involving children of different races and abilities, it demonstrated that different did not mean worse and bigger did not necessarily mean better.

It soon went global and is now screened in more than 140 countries. Unlike McDonald's, here was one form of US cultural hegemony that liberals could embrace because it involved America exporting its best rather than its worst. Not the military, economic and political power that repels, but the diversity, humour, creativity, energy and optimism that attracts.

Even more so because, while they were anxious to preserve the integrity of the Sesame Street brand - two actors dressed as Ernie and Bert were arrested in the Netherlands last year because they did not have permission from the creators - they have not tried to impose uniformity on how the show might be tailored to local needs.

So in Egypt there is Khokha, the education-eager puppet who encourages girls to go to school; China has Xia Mei Zi, the assertive toddler who promotes self-esteem among girls; and the Russian version has Zeliboba, the ancient tree spirit who teaches children there is much to learn from Old Russia. Last month the South African version, Takalani Sesame, was introduced to Kami, a five-year-old orphan with HIV who lives with a foster mother.

As it has spread in influence so has it risen in stature. Last year the UN secretary general, Kofi Annan, appeared on the show and said diplomats could learn a thing or two from its cast. In April one of its characters, Elmo, testified before legislators on Capitol Hill in favour of music teaching in schools. But as its friends have become more powerful so have its enemies. Plans to introduce a similar HIV character into the American version were dropped in August after republican politicians objected with the veiled threat of cutting the partially state-funded show.

But the Street's most thorny problem has been applying its format to areas of conflict. To discover why, we need look no further than Northern Ireland where they are looking to develop a local version. In a recent study, conducted by the University of Ulster, children were shown pictures and objects relating to different communities and asked what they thought of them.

The results were staggering. Almost two-thirds of three-year-old Catholics preferred the Irish flag, while 59% of Protestants preferred the Union Jack. One four-year-old Catholic girl said: "I like the people who are ours. I don't like those ones because they are Orangemen. They're bad people." A Protestant girl of the same age said: "Catholics are the same as masked men. They smash windows." Little wonder then that Sesame Street, which is aimed at precisely that age group, is having trouble setting up there. "It won't be easy. The issues [in Northern Ireland] are extremely complex and we don't pretend to have all the answers. It'll be about finding the right partners," says Gary Knell, the president and chief executive of Sesame Workshop.

For the sake of the region we must hope he succeeds. Research in the Middle East showed that the prejudicial attitudes of children who watched Sesame Street towards those on the other side of the divide softened. In 1993, in the warm glow of the Oslo accords, an Israeli-Palestinian co-production set up a joint venture to screen the show. But, an intifada, several suicide bombers and Israeli military incursions later, the name has been changed to "Sesame Stories" - the notion of a street in the region where people and puppets could mix freely was regarded as untenable, as has the notion that Arab and Israeli children might even become friends. With separate programmes to be made from now on, this illustrates how the show's success is contingent on the political context in which it is shaped.

"Children in Palestine today will not appreciate, understand, absorb and react in a positive way to the goals we want to accomplish," said the Palestinian executive producer, Daoud Kuttab, whose studio in Ramallah was damaged by Israeli soldiers. "You're telling them to be tolerant to Israelis when Israeli tanks are outside their homes."

The best thing parents who want their children to grow up with liberal values can do is make sure there is a liberal world for them to grow up in. Where progressive standards lead, Ernie, Bert and the rest of the crew are sure to follow.

This column was brought to you by the letters P, E, A, C and E, tragically complicated by the numbers 9 and 11. g.younge@theguardian.com